The invention regards a retaining plate for a machine tool work piece, where the machine tool is equipped with a tool, eg. an erosion wire, that can be moved in the z-directon of a work area, and where the work area is bounded by an xy-plane that is perpendicular to the z-axis, and with a work table whose work surface is in a specifc position relative to the xy-plane and which is arranged in the direction of movement of the tool, The invention also regards a machine tool, particularly a wire EDM-machine.
For the purposes of electroerosive machining, particularly for precision small-lot production, it is necessary to transport the chuck-mounted work piece from one processing location to the next without changing work piece alignment, e.g. in an orthogonal system. Retaining plates with reference elements have been developed for use with cavity sinking EDM machines. These retaining plates work together with the mating elements of a machine chuck equipped with a clamping device in order to repeatedly position the work piece with high precision.
In the case of wire EDM-machines, holders of this type cannot be used because the erosion wire gets in the way and thereby prevents their use. It is the purpose of the invention to provide a retaining plate for the machined work piece that allows for any number of work piece transitions without loss of alignment precision during positioning, specifically in the case of wire EDM-machines.
According to the invention, the above-mentioned retaining plate is to have a first planar section that has at least one opening for inserting the work piece, with appropriate retaining devices for the work piece, and with a second section that has elements able to function together with mating elements on the work table chuck in order to permit repeated, precise positioning of the first section in the work area. After mounting the work piece in the opening, its position relative to the retaining plate will remain the same, so that the retaining plate can be transferred any number of times without loss of alignment precision. The retaining plate can be manufactured easily and cheaply because, with the exception of the reference elements, it does not require precision machining. During the machining procedure, most effective use of the work area can be made if the first section is kept at the lowest end of th work area limit, so that even large work pieces can be eroded.
Conveniently, the opening is completely surrounded by the first section; in addition, it is possible to equip the first section with several openings so that the retaining plate can hold several work pieces. Furthermore, it is preferable that a pilot bore be provided for the creation of the opening fitted to the shape of the work piece in the first section. The erosion wire may, for example, be threaded through the pilot bore, and the work piece opening may then be cut out of the first section.
The second section of the retaining plate creates a connection to the machine via the chuck in such a way as to allow not just for easy transfer of the work piece without loss of alignment precision, but also for compensation of positioning differences between work surface and work area, Therefore, depending on the individual machine tool design, the second section is usually offset across the surface expanse of the first section, with a stepped or slanted transition section being provided between the first and second sections of the retaining plate. In an extension of the invention, if the two opposite sides of the second section are equipped with profiles for the grippers of an automatic manipulator, the retaining plate according to the invention may be transferred with the mounted work piece from one work table to another.
Elements and mating elements may be designed according to the specific requirements of one of the known reference systems, such as in [European patents] EP-111092 or EP 255 042, or EP-A-722809. Thus, it is recommended that reference elements be provided on opposite sides, i.e. the top and bottom, of the retaining plate, so that the retaining plate may be turned 180 degrees. The design elements of the invention are indicated in the subordinate claims.
A detailed description of the invention is provided below, using the embodiment shown in the attached drawing.